I know in javascript Objects double as hashes but i have been unable to find a built in function to get the keys
var h = {a:'b',c:'d'};
I want something like
var k = h.keys() ; // k = ['a','c'];
It is simple to write a function myself to iterate over the items and add the keys to an array that I return, but is there a standard cleaner way to do that?
I keep feeling it must be a simple built in function that I missed but I can't find it!
There is function in modern JavaScript (ECMAScript 5) called Object.keys
performing this operation:
var obj = { "a" : 1, "b" : 2, "c" : 3};
alert(Object.keys(obj)); // will output ["a", "b", "c"]
Compatibility details can be found here.
On the Mozilla site there is also a snippet for backward compatibility:
if(!Object.keys) Object.keys = function(o){
if (o !== Object(o))
throw new TypeError('Object.keys called on non-object');
var ret=[],p;
for(p in o) if(Object.prototype.hasOwnProperty.call(o,p)) ret.push(p);
return ret;
}
For production code requiring a large compatibility with client browsers I still suggest Ivan Nevostruev's answer above with shim to ensure Object.keys
in older browsers. However, it's possible to get the exact functionality requested using ECMA's new defineProperty
feature.
As of ECMAScript 5 - Object.defineProperty
As of ECMA5 you can use Object.defineProperty()
to define non-enumerable properties. The current compatibility still has much to be desired, but this should eventually become usable in all browsers. (Specifically note the current incompatibility with IE8!)
Object.defineProperty(Object.prototype, 'keys', {
value: function keys() {
var keys = [];
for(var i in this) if (this.hasOwnProperty(i)) {
keys.push(i);
}
return keys;
},
enumerable: false
});
var o = {
'a': 1,
'b': 2
}
for (var k in o) {
console.log(k, o[k])
}
console.log(o.keys())
# OUTPUT
# > a 1
# > b 2
# > ["a", "b"]
However, since ECMA5 already added Object.keys
you might as well use:
Object.defineProperty(Object.prototype, 'keys', {
value: function keys() {
return Object.keys(this);
},
enumerable: false
});
Original answer
Object.prototype.keys = function ()
{
var keys = [];
for(var i in this) if (this.hasOwnProperty(i))
{
keys.push(i);
}
return keys;
}
Edit: Since this answer has been around for a while I'll leave the above untouched. Anyone reading this should also read Ivan Nevostruev's answer below.
There's no way of making prototype functions non-enumerable which leads to them always turning up in for-in loops that don't use hasOwnProperty
. I still think this answer would be ideal if extending the prototype of Object wasn't so messy.
you can use Object.keys
Object.keys(h)
You could use Underscore.js, which is a Javascript utility library.
_.keys({one : 1, two : 2, three : 3});
// => ["one", "two", "three"]
using jQuery you can get the keys like this:
var bobject = {primary:"red",bg:"maroon",hilite:"green"};
var keys = [];
$.each(bobject, function(key,val){ keys.push(key); });
console.log(keys); // ["primary", "bg", "hilite"]
Or:
var bobject = {primary:"red",bg:"maroon",hilite:"green"};
$.map(bobject, function(v,k){return k;});
thanks to @pimlottc
if you are trying to get the elements only but not the functions then this code can help you
this.getKeys = function() {
var keys = new Array();
for(var key in this) {
if( typeof this[key] !== 'function') {
keys.push(key);
}
}
return keys;
}
this is part of my implementation of the HashMap and I only want the keys, this
is the hashmap object that contains the keys